Sea of sarin: North Korea’s chemical deterrent

North Korea periodically comes into the news as it advances its nuclear and ballistic missile ambitions and continues to employ rhetoric about destroying its enemies. With the Korean Peninsula technically still at war, a growing concern today is that at some point North Korea will acquire the capability to launch a nuclear-armed ballistic missile against the United States or one of its allies. Counterproliferation efforts on the peninsula have had a frustrating history, leading the United States to deploy its Terminal High Altitude Area Defense (THAAD) missile system in South Korea. The US secretary of state, Rex Tillerson, has even suggested the possibility of preemptive military action against the North.

To many analysts of South Korean security, the problem with the preemptive military option is Seoul’s proximity to North Korean artillery placed across the demilitarized zone. North Korea, as a form of strategic deterrence, has periodically threatened to use this artillery to turn Seoul into a “sea of fire.” Lending credence to Pyongyang’s threats are figures from the Global Security website:

“According to one report, a South Korean security analyst suggested that DPRK artillery pieces of calibers 170mm and 240mm ‘could fire 10,000 rounds per minute to Seoul and its environs.’ North Korea has about 500 long-range artillery tubes within range of Seoul, and the total rate of fire of these artillery pieces would be between 2,000 and 4,000 rounds per minute. The DPRK’s [200] 240mm [multiple rocket launchers] fire either 12 or 22 rounds, providing a maximum single salvo of no more than 4,400 rounds.”

Seoul, South Korea’s capital, is the country’s largest and densest population center, with more than 10 million people living in an area of about 600 square kilometers. It is the heart of the world’s fourth-largest metropolitan area and it contains one-fifth of South Korea’s population. It has been estimated that a sustained North Korean artillery attack on Seoul would result in tens of thousands of fatalities if the artillery were armed with conventional high explosives, and in the hundreds of thousands in the case of chemical weapons.

Still, as appalling as these figures appear, they are ultimately figurative, based on vague North Korean threats. It is debatable how many of North Korea’s artillery pieces might be tasked with an attack on Seoul, and if they are within range. Artillery in the demilitarized zone, notes Roger Cavazos of the Nautilus Institute, mostly covers the less densely populated one-third of the city, closer to the DMZ. Using imagery from Google Earth to analyze losses in Seoul due to an artillery attack with high explosives over several days, Cavazos estimates casualties an order of magnitude lower than some others have estimated. While estimates have varied regarding how many artillery pieces the North has, with some estimates running into the thousands, the 700 artillery pieces noted by Global Security is a conservative figure that most analysts have accepted.

Without knowing the details of Pyongyang’s military plans, estimates of the consequences of a North Korean artillery assault are ultimately hypothetical analogies. Where chemical artillery in particular is concerned—because the composition of weapons, payloads, and targets is unknown—the most appropriate analysis of the magnitude of a countervalue threat relies on a heuristic approach. That is, one associates a quantity of sarin with casualty rates based on a generalized application of how chemical weapons operate, rather than performing a simulation of how individual weapons would impact specific targets. Using such an approach, differences in population densities (for example, an attack on Incheon instead of on Seoul) will lower casualty estimates, but will not change the percentage of the targeted population that suffers casualties. Continue reading.